The invention relates to a sputtering apparatus, especially one with a magnetron cathode with rotating target and target cooling performed by a fluid coolant, preferably water.
In sputtering processes, high-power sputtering apparatus are used in practice, among other things, in which a magnetic field in front of the cathode increases the probability of collisions of the particles and hence the probability of their ionization. The heart of these high-power sputtering apparatus is the so-called magnetron cathode.
A magnetron cathode of this kind is described, for example, in German Patent 2417288. This corresponds to U.S. Pat. No. 4,166,018, which is incorporated herein by reference.
In this patent there is described a cathode sputtering apparatus with a high sputtering rate, with a cathode which has on one of its surfaces the material that is to be sputtered and deposited on a substrate, and having a magnet system arranged such that magnetic lines of force issuing from the sputtering surface and returning thereto form a discharge area which is in the shape of a closed loop, and having an anode disposed outside of the paths of the sputtered material and moving from the sputtering surface to the substrate.
In the said patent the cathode surface to be sputtered and facing the substrate to are sprayed be flat, that the substrate is moved across and close to the discharge area, parallel to the flat sputtering surface, and that the magnet system producing the magnetic field is disposed on the side of the cathode facing away from the flat sputtering surface.
The state of the art also includes sputtering apparatus with a rotating magnetron cathode. The prospectus of Airco Coating Technology, A Division of the BOC Group, Inc., identified ACT10110K988, hereinafter called-the "Airco Prospectus," describes the construction and the manner of operation of such a sputtering apparatus, known in itself, which has a rotating magnetron cathode. As it appears from the illustrations and the text of the Airco Prospectus, it is precisely only the cylinder-shaped or tube-shaped target that rotates. The stationary magnet unit of the magnetron cathode is situated in the interior of the target.
Important components of a magnetron cathode of this kind, known in itself, are, among others (see the Airco Prospectus in this regard), in addition to the rotating cylindrical target and the stationary magnet unit, the target drive system, a water cooling system, a vacuum chamber in which the rotating target and the substrate, among other things, are situated, and a power supply unit for the cathode. In practice, the target is applied as a coating to a tube consisting, for example, of copper. The system, consisting of a target coating and copper tube, rotates in front of the burning plasma.
Also pertaining to the state of the art is European patent 0070899, to which U.S. Pat. No. 4,356,073 corresponds (hereby incorporated by reference). In this patent an apparatus for the sputtering of thin films of a selected coating material onto substantially planar substrates is described, consisting of an evacuable coating chamber, a cathode mounted horizontally in this coating chamber and having an elongated, cylindrical tube element on whose outer surface a coating of the coating material to be sputtered has been applied, and magnetic means which are disposed in this tube element in order to provide a sputtering zone extending longitudinally therefrom.
U.S. Pat. No. 4,356,073 discloses means for rotating this tube element about its longitudinal axis in order to bring various parts of the coating material into a sputtering position with respect to the above-mentioned magnet means and inside of the aforesaid sputtering zone, and by means situated in the coating chamber for the horizontal support of the substrates and for transporting them past the magnet means so that these substrates receive the sputtered material.
In particular it can be seen in the drawing entitled "C-MAG.TM. Rotatable Magnetron" in the Airco Prospectus, hereinafter called "Airco Prospectus Drawing," that it is state of the art to feed water as coolant through a water line into the interior of the rotating target. The water in the Airco Prospectus drawing washes around the magnet assembly represented therein.
It can be seen from the Airco Prospectus Drawing that the cross section for the water flow expands quite considerably. The cross section of the feed line of the subject matter of the Airco Prospectus Drawing is significantly less than the flow cross section within the rotating target in the Airco Prospectus Drawing. The velocity of flow of the coolant is accordingly greatly reduced by this enlargement of the flow cross section. In the area of the heating caused by the plasma local overheating can therefore occur, which is extremely disadvantageous to the sputtering process. There is a considerable danger of the formation of steam bubbles.